I got some 1/2" OD 1/4" ID steel light duty reducer bushings from
McMaster-Carr to use as
adapter from a motor shaft to a lawn mower wheel for my new robotics
project. I drilled a small hole perpendicular into it for a "set screw" --
but
am using some 3/4" long "regular" screws from Home Depot since I want it go
through the lawn mower wheel shaft, too. When I tighten it down all it takes
is a small amount of extra force to strip the screw. I am thinking the hole
I drilled before I tapped it is too big, and/or the screw is too soft. (
I'll try another hole tomorrow )

What would I need to ask for in a screw to make sure it is hard enough to
keep it's threads ?

The following URL shows a photo with inset of the bushing and screw for
reference:
http://www.waycoolgear.com/ebay/wheel.jpg